Steering control system for vehicle

ABSTRACT

A steering control section has a first steering angle correction amount calculating section, a second steering angle correction amount calculating section, and a motor rotational angle calculating section. The first correction amount calculating section calculates a first correction amount based on a vehicle speed and an actual steering wheel angle. The second correction amount calculating section calculates a second correction amount through multiplying a control gain corresponding to the vehicle speed with a value calculated by low-pass filtering a differential value of steering wheel angle. The motor rotational angle calculating section calculates a motor rotational angle corresponding to the value adding the first and second steering angle correction amount, and outputs it to a motor driving section so as to drive an electric motor for correcting the steering angle. Thereby, an unstable vehicle behavior due to a resonance of a yaw motion caused in the steering operation can be suppressed.

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/477,347 (now U.S.Pat. No. 7,931,113), filed Jun. 30, 2006, and which application isincorporated herein by reference.

The present application also claims priority from Japanese ApplicationNos. 2005-196722 and 2005-204748, the disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a steering control system for avehicle, more particularly, to a front-wheel steering control system forcorrecting a steering angle of front wheels by an electric motor or thelike.

2. Description of the Related Prior Art

Conventionally, there have been proposed many techniques for correctinga steering angle of front wheels of a vehicle being input by a driver.For example, Japanese Patent Application Laid-Open No. 2004-168166discloses a steering control apparatus with a variable steering gearratio in which a differential factor depending on a steering angularvelocity is shifted from a positive range to a negative range inproportion to an increase of a vehicle speed. Moreover, a steering gearratio thereof is decided by adding a proportional factor depending onthe steering angle and the differential factor as mentioned above.

However, according to the front-wheel steering control apparatus whichcorrects a steering angle only by the vehicle speed and an operation ofthe driver as disclosed in the above mentioned prior art, there arises aproblem that it is difficult to improve a yaw response of the vehicle inassociation with sufficiently suppressing an unstable vehicle behaviordue to a resonance of a yaw movement of steering controls.

SUMMARY OF THE INVENTION

In view of a consideration to the foregoing problem, an object of thepresent invention is to provide a steering control system of a vehiclewhich can securely suppress an unstable vehicle behavior due to aresonance of a yaw movement caused by a steering operation, improving ayaw response of the vehicle.

According to the present invention, there is provided a vehicle steeringcontrol apparatus having a steering upper shaft for inputting a steeringoperating angle, a steering lower shaft for steering front wheels of thevehicle, a steering angle sensor for detecting a steering angle of thesteering upper shaft, and a vehicle speed sensor for detecting a speedof the vehicle. The vehicle steering control apparatus further comprisessteering angle correction calculating means and a steering anglecorrecting mechanism. The steering angle correction calculating meanscalculates a correction amount of a steering angle of the steering lowershaft. Also, the steering angle correcting mechanism is provided betweenthe steering upper shaft and the steering lower shaft for correcting thesteering angle of the steering lower shaft through adding the correctionamount calculated by the steering angle correction calculating means tothe steering angle of the steering upper shaft detected by the steeringangle sensor.

The steering angle correction calculating means calculates a firstcorrection amount of the steering angle of the steering lower shaftbased on the vehicle speed as detected by the vehicle speed sensor, anda second correction amount thereof based on a value obtained throughlow-pass filtering a differential value of the steering angle detectedby the steering angle sensor, wherein a total correction amount of thesteering angle of the steering lower shaft is obtained through addingthe first correction amount based on the vehicle speed detected by thevehicle speed sensor to the second correction amount.

The vehicle steering control apparatus may further comprise a yaw ratesensor for detecting the yaw rate of the vehicle, wherein the steeringangle correction calculating means calculates a third correction amountof the steering angle of the steering lower shaft based on the yaw ratedetected by the yaw rate sensor instead of the second correction amount.

In addition, the vehicle steering control apparatus may further comprisea yaw rate sensor for detecting the yaw rate of the vehicle and atransverse acceleration sensor for detecting the transverse accelerationof the vehicle, wherein the steering angle correction calculating meanscalculates an angular velocity of a vehicle slip based on the yaw rateand the transverse acceleration of the vehicle, and further calculates afourth correction amount of the steering angle of the steering lowershaft based on the angular velocity of a vehicle slip instead of thesecond correction amount. In both the cases of the third and fourthcorrection amounts also, the total correction amount of the steeringangle of the steering lower shaft is obtained through adding either ofthem to the first correction amount based on the vehicle speed.

Thereby, it allows the vehicle steering control apparatus of the presentinvention to improve the yaw response of the vehicle, specifically, tosecurely suppress the unstable vehicle behavior due to the resonance ofyaw movement caused by the steering operation of a user.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome clearly understood from the following description with referenceto the accompanying drawings, wherein:

FIG. 1 is an explanatory view roughly showing a steering control systemof vehicle front wheels according to one embodiment of the presentinvention;

FIG. 2 is a functional block diagram of the vehicle steering controlapparatus as shown in FIG. 1;

FIG. 3 is a flowchart of a program included in the vehicle steeringcontrol apparatus of FIG. 1;

FIG. 4 is a characteristics chart of a steering gear ratio responsive toa vehicle speed according to the present invention;

FIG. 5 is a characteristics chart of a control gain as shown in FIG. 3;

FIG. 6 is a characteristics chart showing a relationship between asteering frequency and a yaw rate gain;

FIG. 7 is an explanatory view roughly showing a vehicle steering controlapparatus according to another embodiment of the present invention;

FIG. 8 is a functional block diagram of the vehicle steering controlapparatus as shown in FIG. 7;

FIG. 9 is a flowchart of a program included in the vehicle steeringcontrol apparatus of FIG. 7;

FIG. 10 is a characteristics chart of the first control gain as shown inFIG. 9;

FIG. 11 is a characteristics chart of the second control gain as shownin FIG. 9;

FIG. 12 is a functional block diagram of a vehicle steering controlapparatus according to the other embodiment of the present invention;and

FIG. 13 is a flowchart of a program included in the vehicle steeringcontrol apparatus as shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred first embodiment of the present inventionwill be described in accordance with FIGS. 1 to 6. As shown in FIG. 1, avehicle steering control apparatus 1 includes a steering wheel 2, and asteering shaft 3 as extended therefrom and connected to a pinion shaft 6extended from a gear box 5 via a joint portion 4 formed by a universaljoints 4 a, 4 a and a joint shaft 4 b.

A tie rod 8 fl is extended from the gear box 5 to a left front wheel 7fl, and on the other hand, another tie rod 8 fr is extended to a frontright wheel 7 fr.

Tie rod ends of the tie rods 8 fl, 8 fr are connected to accelerationhousings 10 fl, 10 fr for freely and rotationally supporting each leftand right wheels 7 fl, 7 fr via knuckle arms 9 fl, 9 fr.

A steering angle correcting mechanism 11 for the front wheels isprovided at a middle portion of the steering shaft 3 to vary a steeringgear ratio. The steering shaft 3 comprises an upper shaft 3U extendingupward from the steering angle correcting mechanism 11 and a lower shaft3L extending downward therefrom.

An explanation about the structure of the steering angle correctingmechanism 11 will be given as follows. A lower portion of the uppershaft 3U and an upper portion of the lower shaft 3L are separately fixedto a pair of sun gears 12U, 12L for rotating about the same rotatingaxis, and the pair of the sun gears 12U, 12L are individually andseparately meshed with planetary gears 14U, 14L fixed on a plurality(for example, three) of pinion shafts 13.

The pair of the sun gears 12U, 12L are stored in a carrier 15 forco-axially supporting the pinion shaft 13, and a driven gear 18 formeshing with a drive gear 17 fixed on an output shaft 16 a of anelectric motor 16 is provided on an outer and upper periphery of thecarrier 15.

The electric motor 16 is driven by a motor driving section 21 which isstructured to rotate the motor 16 in accordance with signalscorresponding to a rotational angle thereof inputted from a steeringcontrol section 20 as correcting means of the front wheel steeringangle.

There are further provided a vehicle speed sensor 31 for detecting avehicle speed V and a steering wheel angle sensor 32 for detecting asteering wheel angle θHd inputted by the driver, and therefore thesignals from the vehicle speed sensor 31 and the steering wheel anglesensor 32 are inputted into a steering control section 20 including asteering angle correction calculating means therein.

Next, the steering control section 20 calculates the correction amountof the front wheel steering angle to be added to the steering wheelangle inputted by the driver on the basis of each input signal describedabove according to a steering control program described later in orderto keep an appropriate vehicle behavior, and then outputs a motorrotational angle θM based on the correction amount to the motor drivingsection 21.

That is, as shown in FIG. 2, the steering control section 20 comprisesmainly a first correction amount calculating section 20 a of the frontwheel steering angle, a second correction amount calculating section 20b of the front wheel steering angle and a motor rotational anglecalculating section 20 c.

The vehicle speed V from the vehicle speed sensor 31 and the steeringwheel angle θHd from the steering wheel angle sensor 32 are inputtedinto the first correction amount calculating section 20 a. And, a firstcorrection amount δHc1 of the steering wheel angle θHd is calculated bythe following equation (1), and is outputted to the motor rotationalangle calculating section 20 c.δHc1=((θHd/ndcl)−(θHd/nd))·nc  (1)

wherein “nd” is a steering gear ratio at the driver side (when theelectric motor 16 is stopped, the steering gear ratio affects a steeringoperation by the driver, which is decided by the pair of the sun gears12U and 12L, the pair of the planetary gears 14U and 14L and thesteering gear box 5.) Also, “nc” is a steering gear ratio at the side ofthe front wheel steering angle correcting mechanism 11 (when the motor16 is driven during no operation of the steering wheel, the steeringgear ratio affects the vehicle, which is decided by the drive gear 17and the driven gear 18). Further, “ndc1” is a vehicle-speed-sensitivesteering gear ratio gained by a preset map and calculating equations.This vehicle-speed-sensitive steering gear ratio “ndcl” is, for example,set as shown in FIG. 4, wherein when the vehicle speed is low, it is setto have a quick responsive characteristics against the driver sidesteering gear ratio “nd”, and also when the vehicle speed is high, it isset to have a slow responsive characteristics against the driver sidesteering gear ratio “nd”.

The vehicle speed V and the steering wheel angle θHd are inputted alsoto the second correction amount calculating section 20 b, where thesecond correction amount δHc2 for the steering wheel angle θHd iscalculated by the following equation (2), and then is outputted to themotor rotational angle calculating section 20 c.δHc2=Gcd·(l/(1+Tcd·S))·(dθHd/dt)/nd  (2)

wherein “Gcd” is a control gain, “Tcd” is a time constant of the lowpass filter, “S” is a Laplace operator, and (dθHd/dt) is a differentialvalue of the front wheel steering angle.

Accordingly, the above equation (2) indicates that the low-passfiltering process is prosecuted to multiply the differential value ofthe front wheel steering angle by the (1/(1+Tcd·S). The time constantTcd in the low pass filtering process is set at a reciprocal of anangular velocity of a resonance oscillation in a yaw motioncorresponding to the inputted steering operating angle, wherein theresonance frequency is in, for example, 1-2 Hz.

Also, since the characteristics with a steep peak for the frequency ofthe steering operation becomes extremely remarkable in proportion withan increase of the vehicle speed V, the control gain Gcd is set at alarger value as the vehicle speed V becomes higher by referring to themaps or the like, as shown in FIG. 5.

The motor rotational angle calculating section 20 c receives the firstcorrection amount δHc1 of the steering wheel angle θHd from the firstcorrection amount calculating section 20 a and the second correctionamount δHc2 of the steering wheel angle θHd from the second correctionamount calculating section 20 b as the inputted value. Then, the motorrotational angle θM is calculated by the following equation (3), and isoutputted to the motor driving section 21.θM=(δHc1+δHc2)·nc  (3)

Next, the steering control program executed by the above mentionedsteering control section 20 will be explained by referring to theflowchart shown in FIG. 3.

First, some desired parameters, namely, the vehicle speed V and thesteering wheel angle θHd inputted by the driver are read at step 101(“step” is abbreviated as “S” in the following description).

Second, at S102, the vehicle-speed-sensitive steering gear ratio “ndcl”is calculated by utilizing the map and/or calculating equations presetin the first correction amount calculating section 20 a.

Next, at S103, the first correction amount calculating section 20 acalculates the first correction amount δHc1 of the steering wheel angleθHd by using the aforementioned equation (1).

Next, at S104, the second front wheel correction amount calculatingsection 20 b calculates the control gain Gcd by using the aforementionedequation (2) or a preset map (e.g., see FIG. 5).

Next, at S105, the second correction amount calculating section 20 bcalculates the second correction amount δHc2 of the steering wheel angleθHd by using the aforementioned equation (2).

Finally, at step S106, the calculating section 20 c of the motorrotational angle calculates the motor rotational angle θM by using theaforementioned equation (3), outputs it to the motor driving section 21,and then exits the program.

The effect of the present embodiment will be explained hereinafter. Asshown in FIG. 6, the “conventional characteristics 1”, which has no peakvalue with regard to the steering frequency, has the following features,that is, the response to a quick steering operation is very stable, butdull, in other words, there occurs a problem that a performance foravoiding a danger is inferior. On the contrary, in the “conventionalcharacteristics 2”, which has a steep peak value with regard to thesteering frequency, there occurs a problem that the vehicle is easy tospin and is apt to be very unstable when changing over a direction tosteer at a vicinity of the resonance frequency of the yaw moment.Accordingly, the low-pass filtering operation for the differential value(dθHd/dt) of the front wheel steering angle allows the steeringfrequency to gradually increase the gain and have no apparent peakvalue, which is the feature according to the first embodiment of thepresent invention, so that an improvement of a response ability for aquick steering operation and a stable control ability (an avoidance ofthe spin) can be realized. Specifically, the yaw response of the vehiclecan be securely improved, and also the unstable vehicle behavioraccording to the resonance of the yaw movement in the steering operationcan be securely suppressed.

Additionally, noise elements which may be included in the differentialvalue (dθHd/dt) of the front wheel steering angle can be effectivelyeliminated by the low-pass filtering operation.

The second embodiment of the present invention will be explainedhereinafter with FIGS. 7-11. Moreover, the second embodiment relates toa second front wheel steering angle correction amount calculatingsection 30 where the second correction amount is calculated on the basisof a slip angular velocity of the vehicle comprising a yaw rate and atransverse acceleration. Since the other elements and functions aresubstantially the same as ones of the first embodiment, the same symbolsare given to the same elements as ones of the first embodiment, and therespective explanations thereof are omitted.

As shown in FIG. 7 which is an explanatory view roughly illustrating avehicle steering control apparatus according to another embodiment, avehicle behavior control apparatus 40 is mounted on the vehicle ascontrol means of a vehicle behavior. The vehicle behavior controlapparatus 40 is, for example, a braking force control apparatus forgenerating a yaw moment to the vehicle by adding a braking force to aselected wheel. Concretely, the vehicle behavior control apparatus 40calculates a target yaw rate on the basis of the vehicle speed and thesteering angle of the front wheels by using an equation of motion of thevehicle. Then, it is decided whether the present vehicle runningcondition is in an over-steering condition or in an under-steeringcondition through comparing an actual yaw rate with the targeted yawrate. As the result, the braking force is applied to an outside frontwheel while turning in order to correct the over-steering condition, andalso the braking force is applied to an inside rear wheel while turningin order to correct the under-steering condition. Further, the vehiclebehavior control apparatus 40 is not limited to one using the brakingforce control apparatus as mentioned above, but it may be one using adriving force distributing apparatus for left or right driving wheels.

The vehicle is further provided with a yaw rate sensor 33 and atransverse acceleration sensor 34 in addition to the vehicle speedsensor 31 and the steering wheel angle sensor 32, signals from which aretransmitted to a steering control section 30. The yaw rate sensor 33detects an actual yaw rate γ of the vehicle, and the transverseacceleration sensor 34 detects an actual transverse acceleration(d²y/dt²) thereof.

The steering control section 30 calculates the correction amount of thefront wheel steering angle added to the actual steering wheel angleinputted by the driver based on each inputted signal in accordance withthe steering control program as described later to adequately keep thevehicle behavior, and outputs the signal of motor rotational angle θM tothe motor driving section 21.

More specifically, as shown in FIG. 8, the steering control section 30is mainly constructed by the first correction amount calculating section20 a, a second correction amount calculating section 30 b, the motorrotational angle calculating section 20 c, and a steering wheel angleoutput value calculating section 30 d.

In the same fashion as the first embodiment, the vehicle speed V isinputted from the vehicle speed sensor 31 and the steering wheel angleθHd from the steering angle sensor 32 are inputted into the firstcorrection amount calculating section 20 a. Further, the firstcorrection amount δHc1 of the steering wheel angle θHd is calculated bythe same following equation (1) as described in the first embodiment,and is outputted to the motor rotational angle calculating section 20 cand the steering wheel angle output value calculating section 30 d.δHc1=((θHd/ndcl)−(θHd/nd))·nc  (1)

The explanation for each element of the above equation (1) is omittedsince the respective elements are the same as ones of the firstembodiment.

Next, the vehicle speed V is inputted from the vehicle speed sensor 31to the second correction amount calculating section 30 b also. Further,the actual yaw rate γ from the yaw rate sensor 33 and an actualtransverse acceleration (d²y/dt²) from the transverse accelerationsensor 34 are inputted into the second calculating section 30 b. Then,the second correction amount δHc2 of the steering wheel angle θHd iscalculated by the following equation (4), and is outputted to the motorrotational angle calculating section 20 c.δHc2=Gcg1·Gcg2·(dβ/dt)  (4)

wherein (dβ/dt) is an angular velocity of a vehicle slip, and iscalculated by the following equation (5).(dβ/dt)=γ−((d ² y/dt ²)/V)  (5)

Further, “Gcg1” in the equation (4) is a first control gain, which isset beforehand by, for example, an experiment and a calculation thereonas shown in FIG. 10. This map is set by the following equation (6) inthe range where the vehicle speed V is higher than the value of Vcl.Gcg1=1/Gγ  (6)

wherein “Gγ” shows a yaw rate gain for the steering angle, and iscalculated by the following equation (7).Gγ=(1/(1+A·V ²))·(V/(1·nc))  (7)

wherein “A” is a stability factor, and “1” is a wheel base.

The first control gain Gcg1 in the range below the value Vc1 in the mapof FIG. 10 is set as a linear to become smaller as the vehicle speedbecomes lower. The reason is that since, in a low speed range, the yawrate gain Gγ becomes small, while the first control gain Gcg1 becomestoo large, if not set like FIG. 10, so that a calculation accuracy forthe angular velocity of the vehicle slip becomes low.

As described above, through setting the first control gain Gcg1 in viewof the yaw rate gain Gγ, a yaw rate gain per a unit of steering anglecorrection becomes constant, so that an interference degree of thecontrol for the steering operation at the high and low speeds can bekept constant.

Further, Gcg2 in the above described equation (4) is a second controlgain, which is set beforehand from, for example, the predeterminedexperiments and calculations as shown in FIG. 11. This second controlgain Gcg2 is set in accordance with the angular velocity (dβ/dt) of thevehicle slip according to the map, in which the value of Gcg2 is set at“0” (zero) in the range where an absolute value of the angular velocity(dβ/dt) is small. Accordingly, when this second control gain Gcg2 ismultiplied as shown in the equation (4), the second correction amountδHc2 of the steering wheel angle θHd becomes 0 (zero) in the small rangeof the vehicle slip angular velocity. In other words, the abovedescribed equation (4) causes a dead zone for the angular velocity(dβ/dt) of the vehicle slip. In this way, unnecessary controls can beavoided by providing the dead zone in the range of the small angularvelocity (dβ/dt) of the vehicle slip.

Then, the motor rotational angle calculating section 20 c receives thefirst correction amount δHc1 of the steering wheel angle θHd from thefirst correction amount calculating section 20 a and the secondcorrection amount δHc2 thereof from the second correction amountcalculating section 30 b. Afterwards, the motor rotational angle θM iscalculated by the following equation (3) which is identical with that ofthe first embodiment, and is outputted to the motor driving section 21.θM=(δHc1+δHc2)·nc  (3)

The steering wheel angle output value calculating section 30 d receivesthe respective signals of the steering wheel angle θHd from the steeringwheel angle sensor 32 and the first steering angle correction amountδHc1 of the front wheel from the correction amount calculating section20 a. And then, the steering wheel angle output value calculatingsection 30 d outputs a steering wheel angle θHout to the vehiclebehavior control apparatus 40 after calculating it by the followingequation (8).θHout=θHd+δHc1·nc  (8)

That is, the above described equation (8) does not contain the value ofδHc2·nc, which is the correction amount according to the vehicle slipangle speed (dβ/dt), so that the control with the vehicle behaviorcontrol apparatus 40 can be properly executed without intervening withthe correction control by the steering control section 30.

Next, a steering control program executed by the above mentionedsteering control section 30 will be explained with the flowchart shownin the FIG. 9.

First, at S201, such required parameters as the vehicle speed V, thesteering wheel angle θHd inputted by the driver, an actual yaw rate γ,and an actual transverse acceleration (d²y/dt²) are read out.

Next, at S202, the vehicle-speed-sensitive steering gear ratio ndcl iscalculated by the preset map and/or equation set in the first correctionamount calculating section 20 a.

Next, at S203, the first correction amount calculating section 20 acalculates the first correction amount δHc1 of the steering wheel angleθHd by using the aforementioned equation (1).

Further, at S204, the second correction amount calculating section 30 bcalculates the vehicle slip angular velocity (dβ/dt) by using theaforementioned equation (5).

Furthermore, at S205, the second correction amount calculating section30 b calculates the first control gain Gcg1 on the basis of any mappreset by the experiments, calculations, or the like.

At step S206, the second calculating section 30 b calculates the secondcontrol gain Gcg2 also in the same fashion as the first control gainGcg1.

Next, at S207, the second correction amount calculating section 30 bcalculates the second correction amount δHc2 by using the aforementionedequation (4).

Then, at S208, the motor rotational angle calculating section 20 ccalculates the motor rotational angle θM by using the equation (3), andoutputs it to the motor driving section 21.

And finally, at step S209, the steering wheel angle output valuecalculating section 30 d calculates the steering wheel angle θHout byusing the aforementioned equation (8), outputs it to the vehiclebehavior control apparatus 40, and then exits the program.

In this way, according to the second embodiment of the presentinvention, since the steering angle correction amount is calculatedthrough adding the first correction amount δHc1 based on the vehiclespeed to the second correction amount δHc2 based on the angular velocity(dβ/dt), a yaw response of the vehicle can be improved and also anunstable vehicle behavior due to a resonance of yaw movement caused bythe steering operation can be securely suppressed.

Additionally, since the steering wheel angle θHout to be outputted intothe vehicle behavior control apparatus 40 does not include the secondcorrection amount δHc2 based on the vehicle slip angular velocity(dβ/dt), the control by the vehicle behavior control apparatus 40 doesnot intervene the control by the steering control section 30, so that itis possible to attain an effective and stable vehicle control.

Lastly, FIGS. 12 and 13 show the third embodiment of the presentinvention. FIG. 12 is the functional block diagram of a steering controlsection 25, and FIG. 13 is the flowchart of a steering control programthereof. Moreover, the third embodiment relates to the steering controlsystem 25 where the second correction amount is calculated on the basisof an actual yaw rate γ. Since the other elements and functions aresubstantially the same as ones of the first and second embodiments, thesame symbols are given to the same elements as ones of the firstembodiment, and the respective explanations thereof are omitted.

More specifically, the steering control section 25 receives the signalsof the vehicle speed V from the vehicle speed sensor 31, the steeringwheel angle θHd inputted by the driver from the steering angle sensor 32and the actual yaw rate γ from the yaw rate sensor 33.

Then, the steering control section 25 calculates the front wheelsteering angle correction amount to be added to the steering wheel angleθHd inputted by the driver based on each inputted signal as mentionedabove according to a steering control program as described later inorder to properly maintain the vehicle behavior, and afterwards thesignal of the motor rotational angle θM is transmitted to the motordriving section 21.

The steering control section 25 has mainly the first correction amountcalculating section 20 a, a second correction amount calculating section25 b, the motor rotational angle calculating section 20 c, and asteering wheel angle output value calculating section 30 d as shown inFIG. 12.

The second correction amount calculating section 25 b of the front wheelsteering wheel angle θHd receives the signals of the vehicle speed Vfrom the vehicle speed sensor 31, and the actual yaw rate γ from the yawrate sensor 32. Then, the second correction amount δHc2 is calculated byusing the following equation (9), and outputted to the motor rotationalangle calculating section 20 c.δHc2=−Gcgl·γ  (9)

As shown in the flowchart of FIG. 13, the steering control programproceeds to S304 after calculating the first correction amount δHc1 ofthe steering wheel angle θHd at S303. At S304, the second correctionamount calculating section 25 b calculates the first control gain Gcg1on the basis of the map preset by the experiments, calculations or thelike in advance, that is, which is set in the same fashion as one of thesecond embodiment.

Next, the program proceeds to S305, and then the second correctionamount calculating section 25 b calculates the second correction amountδHc2 of the steering wheel angle θHd by the aforementioned equation (9).And further, the program proceeds to S306 where the motor rotationalangle calculating section 20 c calculates the motor rotational angle θMwith the aforementioned equation (3), and outputs the result to themotor driving section 21.

Lastly, the program proceeds to S307 where the steering wheel angleoutput value calculating section 30 d calculates the steering wheelangle θHout in accordance with the aforementioned equation (8) and thenoutputs the result to the vehicle behavior control apparatus 40, andafterwards exits the program.

In this way, according to the third embodiment of the present invention,the same effect as the other embodiments thereof can be also attained.

Although the calculated steering wheel angle θHout without the secondcorrection amount δHc2 is outputted to the vehicle behavior controlapparatus 40 according the second and third embodiments, the calculatedsteering wheel angle θHout including the second correction amount δHc2may be also outputted thereto in the case of a vehicle having no vehiclebehavior control apparatus 40 or in the case of characteristics beingable to ignore the interference between the correction executed by thesteering control section 20, 25 and itself.

While there has been described what are at present considered to bepreferred embodiments of the present invention, it will be understoodthat various modifications may be made thereto, and it is intended thatthe appended claims cover all such modifications as fall within the truespirit and scope of the present invention.

1. A vehicle steering control apparatus, comprising: a steering uppershaft for inputting a steering operating angle; a steering lower shaftfor steering front wheels of the vehicle; a steering angle sensor fordetecting a steering angle of said steering upper shaft; a yaw ratesensor for detecting a yaw rate of the vehicle; a vehicle speed sensorfor detecting a vehicle speed, a steering angle correction calculatingmeans for calculating a correction amount of a steering angle of saidsteering lower shaft, said correction calculating means including afirst correction amount calculating section which determines a firstcorrection component of said steering angle based on input as to thesteering angle and vehicle speed, and a second correction amountcalculating section which determines a second correction component basedon input as to the vehicle speed and a yaw rate detected by said yawrate sensor; a steering angle correcting mechanism provided between saidsteering upper shaft and said steering lower shaft for correcting saidsteering angle of said steering lower shaft through adding saidcorrection amount calculated by said steering angle correctioncalculating means to said steering angle of said steering upper shaftdetected by said steering angle sensor; wherein a total correctionamount of said steering angle of said steering lower shaft is obtainedthrough combining said first and second correction components, whereinsaid yaw rate based correction component is obtained by multiplying acontrol gain calculated based on a change of a yaw rate corresponding tosaid vehicle speed to said yaw rate, and wherein said first correctioncomponent features a transition location between a quick steeringresponse characteristic and a slower steering response characteristicthat is based on the vehicle speed, and wherein said yaw rate basedcorrection component is inclusive of a linear relationship betweenvelocity and gain for a velocity range that is inclusive of a velocityrange that comprises said transition location of said first correctioncomponent.
 2. A vehicle steering control apparatus, comprising: asteering upper shaft for inputting a steering operating angle; asteering lower shaft for steering front wheels of the vehicle; asteering angle sensor for detecting a steering angle of said steeringupper shaft; a yaw rate sensor for detecting a yaw rate of the vehicle;a transverse acceleration sensor for detecting a transverse accelerationof the vehicle; a vehicle speed sensor for detecting a vehicle speed, asteering angle correction calculating means for calculating a correctionamount of a steering angle of said steering lower shaft, said correctionamount including an angular velocity based correction component of saidsteering angle of said steering lower shaft based on an angular velocityof a vehicle slip which is calculated based on said yaw rate and saidtransverse acceleration of the vehicle; and a steering angle correctingmechanism provided between said steering upper shaft and said steeringlower shaft for correcting said steering angle of said steering lowershaft through adding said correction amount calculated by said steeringangle correction calculating means to said steering angle of saidsteering upper shaft detected by said steering angle sensor, wherein atotal correction amount of said steering angle of said steering lowershaft is obtained through combining a vehicle speed based firstcorrection component, which is based on said vehicle speed detected bysaid vehicle speed sensor, and said angular velocity based correctioncomponent, wherein said first correction component features a transitionlocation between a quick steering response characteristic and a slowersteering response characteristic that is based on the vehicle speed,wherein said angular velocity based correction component represents asecond correction component and is obtained by multiplying a firstcontrol gain calculated based on a change of a yaw rate corresponding tosaid vehicle speed to said angular velocity of the vehicle slip, andwherein said first control gain is based on a linear relationshipbetween the change of yaw rate corresponding to vehicle speed for avehicle speed below a pre-set vehicle speed value.
 3. The vehiclesteering control apparatus according to claim 2, wherein a range of saidangular velocity of the vehicle slip being less than a predeterminedvalue is in a dead zone.
 4. The vehicle steering control apparatusaccording to claim 2 wherein said first control gain includes anon-linear, decreasing relationship between the change of yaw ratecorresponding to vehicle speed for a vehicle speed above the pre-setvehicle speed value.
 5. The vehicle steering control apparatus accordingto claim 4 wherein said angular velocity based correction component isobtained by multiplying the first control gain and a second controlgain, with the second control gain being set at a lower value when anabsolute value of said angular velocity of vehicle slip is below a firstpre-set threshold value and the second control gain is set at a highervalue when the absolute value is at a higher value than the firstpre-set threshold value.
 6. The vehicle steering control apparatusaccording to claim 5 wherein the second control gain is set to zerowithin a dead zone range wherein said angular velocity of the vehicleslip is below a second pre-set threshold value less than the firstpre-set threshold value.
 7. The vehicle steering control apparatusaccording to claim 2 wherein said angular velocity based correctioncomponent is obtained by multiplying the first control gain and a secondcontrol gain, with the second control gain being set at a lower valuewhen an absolute value of angular velocity of vehicle slip is below afirst pre-set threshold value and the second control gain is set at ahigher value when the absolute value is at a higher value than the firstpre-set value.
 8. The vehicle steering control apparatus according toclaim 7 wherein the second control gain is set to zero within a deadzone range wherein said angular velocity of the vehicle slip is below asecond pre-set threshold value less than the first pre-set thresholdvalue.
 9. The vehicle steering control apparatus according to claim 2,wherein said steering angle correction calculating means furthercomprises a first correction amount calculation section that determinesthat first correction component, a second correction amount calculatingsection that determines the second correction component, and a steeringwheel angle output value calculating section which receives the firstcorrection amount from said first correction amount calculating sectionand is configured to output a steering wheel angle value to a vehiclebehavior control apparatus, and said steering wheel angle output valuecalculating section is arranged relative to said second correctionamount calculating section such that control associated with the vehiclebehavior control apparatus does not intervene control by the steeringcontrol apparatus.
 10. A vehicle steering control apparatus, comprising:a steering upper shaft for inputting a steering operating angle; asteering lower shaft for steering front wheels of the vehicle; asteering angle sensor for detecting a steering angle of said steeringupper shaft; a yaw rate sensor for detecting a yaw rate of the vehicle;a steering angle correction calculator that calculates a correctionamount of a steering angle of said steering lower shaft, said correctionamount including a yaw rate based correction component of said steeringangle of said steering lower shaft based on said yaw rate detected bysaid yaw rate sensor; and a steering angle correcting mechanism providedbetween said steering upper shaft and said steering lower shaft forcorrecting said steering angle of said steering lower shaft throughadding said correction amount calculated by said steering anglecorrection calculator to said steering angle of said steering uppershaft detected by said steering angle sensor, and wherein said yaw ratebased correction component is obtained by multiplying a first controlgain, a second control gain and an angular velocity of vehicle slip,with the first control gain being determined based on a yaw rate gainfor the steering angle, and with the second control gain being set isaccordance with an angular velocity of the vehicle slip such that, whenan absolute value of said angular velocity of the vehicle slip is belowa first pre-set threshold value, the second control gain is set at alower value, and the second control gain is set at a higher value thanthe lower value when the absolute value is at a higher value than thepre-set threshold value.
 11. The vehicle steering control apparatusaccording to claim 10, further comprising a vehicle speed sensor, andwherein a total of the correction amount of said steering angle isobtained by combining a vehicle speed based first correction componentwith said yaw rate based correction component as a second correctioncomponent, and wherein said steering angle correction calculator furthercomprises a first correction amount calculation section that determinesthat first correction component, a second correction amount calculatingsection that determines the second correction component, and a steeringwheel angle output value calculating section which receives the firstcorrection amount from said first correction amount calculating sectionand is configured to output a steering wheel angle value to a vehiclebehavior control apparatus, and said steering wheel angle output valuecalculating section is arranged relative to said second correctionamount calculating section such that control associated with the vehiclebehavior control apparatus does not intervene control by the steeringcontrol apparatus.